Means for determining the primaries



July 4, 1939- F. L. wuRzBuRG. JR 2,165,169

MEANS FOR DETERHINING THE FRIMARIES IN A SYSTEM 0F COLOR REPRODUCTION BYPRINTING Original Filed Sept. 28, 1936 ATTORNEY Patented July 4, 1939MEANS FOR DETERMINING THE PRIMARIES IN A SYSTEM OF COLOR REPRODUCTION BYPRINTING Francis Lewis Wrzburg, A."r., Bronxville, N.l Y.,

assignor to lnterchemical Corporation, a cor poration of OhioApplication September-28, 1936, Serial No; 102,957 Renewed October l1,1938 5 Claims.

This invention relates to means for determining the primaries in asystem of color reproduction by printing.

In co-pending application of Arthur C. Hardy.'

5 Serial No. 99,416, filed September 4, 1936, there is described andclaimed a method for determining the primaries of a color reproductionsystem. In that method, use may be made of a differential print to.compare the color of a specified combination of colored materials withthe color of other combinations in each of which the amount of one ofthe colored materials differs by a small increment from its amount inthe specified comb-ination.

15 In applying this method to determine the primaries of a reproductionsystem by half-tone printing or other printing where definite screenlines or grain lines occur on the printing blocks used ior'the differentcolored inks, the occurthe form of an equilateral triangle consisting oftwo printing areas, one of which is a triangular area in one corner ofthe printing surface con- 35 stituting one-fourth of the whole printingsurface, and the other of which is a trapezoidal area containingthree-fourths of the Whole printing surface. The printing surface .is soformed that the density of the ink printed by the triangular area isslightly different from that printed by the trapezoidal area. I mostdesirably provide a set of such printing blocks in all of which thescreen or grain lines make the same angle with the base ofthe'trapezoidal area.

My invention includes also the triangular and hexagonal differentialprints which may be formed by such printing blocks.

The accompanying drawing shows speciiic printing blocks and printsillustrating my invention. In the drawing:

Fig. 1 is a perspective view of a printing block;

Figs. 2, 3 and 4 show three impressions from the block shown in Fig. 1;

Fig. 5 shows diagrammatically a print made by superposing the threeimpressions shown in Figs. 2, 3 and 4;

Fig. 6 shows six printing blocks assembled as a hexagon; and

Fig. 7 shows diagrammatically a hexagonal differential print made fromthe printing blocks shown in Fig. 6.

'I'he printing block I0 shown in Fig. 1 is a halftone plate having aprinting surface in the form of an equilateral triangle. The printingsurface is provided with the usual projections for printing half-tonedots.

The dot density of the printing surface, which I dei-lne as theproportion of the printed area which is covered by ink from the dots, isdiiferent in different parts of the triangular printing surface. Theprinting surface consists of a triangular area s occupying one-quarterof theY total printing surface, and a contiguous trapezoidal area moccuping three-quarters of the printing surface. The dot density of theprinting surface in the triangular area s is slightly different from thedot density in the trapezoidal z ea 1n. The screen lines, which may beregarded as illusl trated by the dotted lines shown in Fig. 1, run inthe same direction throughout the printing surface. In the formillustrated, these lines make an angle of about 45 with the base of thetrape- I sity of the printing surfaces of the different blocks may beselected as desired, but in each block the density of the triangulararea is slightly diiierent from that of the trapezoidal area.

Fig. 5 shows diagrammatically a diierential print which may be made fromthree impressions of the block shown in Fig. 1 or by one impression'ofthis block and two impressions from corresponding blocks. In making thediierential print shown in Fig. 5, three impressions' of the blockIshown in Fig. l made in dierent colors may be superposed. 'Ihe way inwhich the block is turned in making the three impressions is shown inFigs. 2, 3 and 4. From these figures, it

is apparent that betweenthe rst and second impressions the block isrotated 120 to the left, and between the second and third impressionsthe block is rotated 240 to the right, that is, it is turned 120 to theright from the position which it had in the first impression, From thisturning of the block, it results that the screen lines in the threesuperposed impressions cross each other at wide angles so that there isnov moir effect. This procedure and the form of the blocks also resultin making a symmetrical differential print having central area A andthree outer areas B, C, D, all four of equal size, and

so arranged that the combination of the colored inks in each one of theouter areas B, C, D is like the combination of the inks in the centerarea except for a slight diierence in the density of one of the threecolored inks. Such a, print is have a dot density of seventy per cent.in their trapezoidal areas and a dot density of eighty per cent. intheir triangular areas, and three similar printing blocks 20, in each ofvwhich the density of the trapezoidal area m is zero and that of thetriangular area s isa small increment above zero. for example, flve percent. The six printing blocks may be assembled in the form of a regularhexagon as shown'in Fig.`6.

Three differently colored impressions from the assembledA blocks arethen made with a turning of the assembled blocks corresponding to theturning of the single blocks. already described in connection withFigs.`2"to 5.

This procedure produces the hexagonal differential print shown in Fig.7, containing twentyfour equal triangular areas of different colors.Assuming that the three impressions were made with yellow, magenta andblue-green inks, the area AI `shows the color of the yellow ink, the

larea A3 the color of the magenta ink, and the area A5 the color of theblue-green ink. The intermediate areas A2, A4, A6 show the colorsproduced by combining pairs of the inks in equal proportions. vA2 showsthe color of a combination of the yellow and magenta inks, A4 of acombination of the magenta and blue-green inks, and A6 of a combinationof the blue-green and yellow inks. f

The areas Bl, CI, Dl'show the changes in the color of the area AI whichare produced by adding separately 'a small increment of each of thethree colored inks, and they same is true of the areas surrounding eachofl the triangles from A2 to A6. 'Ihe density of eachv colored ink ineach area is indicated in the following table:

lBy comparing the colors of the surrounding triangles with the colors ofthe triangles AI to A6, the primaries of the system for six dierentcolored areas may be determined as described in the application ofArthur C. Hardy aforementioned. v f

`Ii.' desired. the plate for printing the print shown in Fig. 'I may bemade in a single piece, instead of by assembling triangular printingblocks.

what I claim is: 1. Means for use in determining the primaries of a color reproduction system by printing. comprising a. printing blockhaving a lined printing surface in the form of an equilateral triangle,said surface being so formed as to print a different density of ink fromtwo parts of its printing surface, which consist respectively of anequilateral triangular area constituting one-quarter of the printingsurface and a contiguous trapezoidal area constituting three-quarters ofthe printing surface, the lines being parallel throughout the wholeprinting surface.

2. Means for use in determining the primaries of a color reproductionsystem by printing, comprising a half-tone printing plate having a tri='and three adjacent triangular areas in'each oneof whichA two of thecolored inks have the same density as in the central area and onecolored ink has a density slghtly diierent from that which it has in thecentral area, the lines of the three impressions crossing each other atangles of 60.

4. A differential print for determining theprimaries of a colorreproduction system, consisting of superposed impressions of threedifferently colored inks having the form of a hexagon containingtwenty-four equal differently colored areas, each in the form of anequilateral triangle, including six spaced triangular areas and six setsof three triangular areas surrounding each of said six areas and showingthe effect of an increment of one of the colored inks onthe color of thearea which they surround. f

5. A differential print Afor determining the primaries of a colorreproduction system, consisting of superposed impressions of threediiferently colored inks having the form of a hexagon containingtwenty-four equal differently colored areas, each in the form of anequilateral triangle, including six triangular areas showing the colorsproduced by each of the three inks separately and each of the pair ofthe three inks in equal proportions, and six sets of three triangularareas surrounding each of said six areas and showing the colors producedby changing the color of the area which they surround by increments yofeach one Y

